DE60209635T2 - Method and apparatus for printing gray tones using curable inks - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The The present invention relates to ink-jet printing, and more particularly printed media, a printing method and apparatus for printing of pictures with shades of gray varying intensity, especially for printing on transparencies used for production high-quality medical images such as x-rays, ultrasound images, Nuclear medicine images, KMR images, computed tomography images, positron emission tomography images and angiographic images. Under gray tones understand black and white steps and or color levels of varying intensity.

GENERAL STATE OF THE ART

at Medical imaging is the printing of images with one resolution of at least 300 dpi and 256 distinguishable gray levels required, so that the viewer has enough high detail in the medical picture gets to see.

in the There are generally three methods that use a grayscale in an image can be obtained: area modulated pressure, density modulated Pressure or a combination of area modulated pressure and density modulated Print.

at flächenmoduliertem Printing is obtained in grayscale by giving predetermined digits of a Print media to be printed and other places remain unprinted. It uses ink of unlimited density. On the Medium incident light penetrates through the non-printed areas Through, however, is completely absorbed in the printing surfaces by the ink. For this Type of image printing are available various methods: it can a single pixel with different point sizes, different Pixels with a single point size or different pixels used with different point sizes become.

In US Pat. No. 6,102,513 discloses a method and apparatus for printing an output image on a receiving medium according to an input image file defined by a plurality of pixels. Each pixel receives a pixel value. The apparatus includes a printhead having a plurality of nozzles. Each nozzle is capable of ejecting numerous droplets of ink from the nozzle. The centers of different sized ink droplets are deposited in the middle of a pixel on the receiving medium. In this way, ink dots of different diameters or sizes are arranged symmetrically within the pixels on the receiving medium.

bezogen auf die Auflösung, positioniert werden müssen. Dies entspricht 2,7 μm bei 300 dpi. Bei niedrigerer Genauigkeit (d.h. der Abstand zwischen zwei Punkten beträgt mehr als 2,7 μm bei einem 300 dpi-Bild) entsteht sichtbare Streifenbildung.An area modulated printing process is not the most suitable method for printing 256 shades of gray at 300 dpi on a transparency. The pressure points must be tiny (less than 10 μm) to be below the Kanamori curve. This curve takes into account the non-linearity of the sensitivity of the human eye. If an area having a first density is within a second density area and the density difference between both areas is below the Kanamori curve, then the first density area can not be distinguished from the second density area. Furthermore, the points are very precise to position. To achieve a density of 3 with an ink of unlimited density, an area equal to 1 / 1,000th of the pixel should not be printed (white area) because the density / translucency ratio equals T = 10 ^-D , where D represents the density and T the transparency. This means that the droplets with an accuracy of

based on the resolution, must be positioned. This corresponds to 2.7 μm at 300 dpi. At lower accuracy (ie, the distance between two dots is more than 2.7 μm for a 300 dpi image) visible banding occurs.

Density modulated printing is a second method of printing a gray-tone image. In this method, gray levels are obtained by printing equally sized dots of different ink density. A different ink density is obtained by reducing the transparency of the ink for predetermined points. Depending on the ink density or ink color, light will penetrate through the ink to a predetermined extent. Because it is impossible to use 256 heads, each with a different ink print, the ink must be mixed during printing. Mixing may be done prior to ejection from the nozzle as described, for example, in US Pat US 5,606,351 or US 6,097,406 , or after spraying on the medium as described in US 5,889,538 and US 5,625,397 ,

In US 5,889,538 Different colored ink droplets are sprayed onto a printing medium where they fuse and form a dot of the desired color. Each ink droplet contains an amount of ink corresponding to printing data, and is ejected for one of the periods corresponding to the amount of ink contained in the droplet. A controller controls the ink pressure chamber of the printing apparatus so that the ejection of the ink droplets from the ink pressure chamber is performed in accordance with the printing data. The described method involves the disadvantage that the amount of ejected ink and the ejection time must be controlled with extreme accuracy.

In US 5,625,397 For example, various same-color inks having different densities are used in a dot-by-dot printing format for printing on a receiving medium. In this way, a desired optical density can be obtained quickly.

In WO 00/30856 becomes a special primer layer for wet-on-wet printing used in graphic applications, with a uniform and reproducible coalescence of the ink drops is obtained. at high-resolution However, such property is to be avoided in medical images.

disadvantage The above method is that only a limited number of grayscale can be obtained.

SHORT PRESENTATION THE PRESENT INVENTION

task the present invention is the printing of a plurality of gray levels, preferably at least 256, on print media, such as transparencies, the used printing materials, such as inks, not high Absorb dimensions.

task the present invention is the printing of a plurality of gray levels, preferably at least 256, whose densities are uniform over the throughout the density range are distributed, thus accommodating the Kanamori curve is, i. to obtain a quantization of the density values, in the density gradations between a first density value and a second density value corresponding to successive gray level values, less than or equal to the minimum perceivable density difference are.

A Another object of the present invention is the provision a printer and a printing process with which a variety of gray levels, preferably at least 256, can be printed the grayscale densities evenly over the throughout the density range are distributed, thus accommodating the Kanamori curve is, i. to obtain a quantization of the density values, in the density gradations between a first density value and a second density value corresponding to successive gray level values, less than or equal to the minimum perceivable density difference are.

• 1. Drucken des Bildes, unter Verwendung der strahlungshärtbaren Zusammensetzung, in Form von zumindest einem Satz von gegenseitig interstitiell gedruckten Teilbildern, wobei jedes Teilbild aus einem Satz von Punkten besteht, ein Punkt aus einer Anzahl überlagerter Tröpfchen zusammengesetzt ist und jedes Tröpfchen aus einer mehrerer strahlungshärtbarer Zusammensetzungen zusammengesetzt ist, wobei die Tröpfchen auf dem Druckmedium verschmelzen und dabei den Punkt mit vorgegebener Graustufe bilden, und
• 2. vor dem Drucken eines nächsten Teilbildes aus dem Satz von Teilbildern, Bestrahlung der Punkte des vorigen interstitiell gedruckten Teilbildes, um sie aktiv wanderungsbeständig zu machen.
• Gelöst werden die Aufgaben der vorliegenden Erfindung ebenfalls durch eine wie im nachstehenden Anspruch 10 definierte Vorrichtung, mit der unter Verwendung strahlungshärtbarer Zusammensetzungen ein Bild auf einem Druckmedium gedruckt wird, wobei die Vorrichtung folgende Komponenten enthält:
• 3. einen Druckkopf, mit dem unter Verwendung der strahlungshärtbaren Zusammensetzung das Bild in Form von zumindest einem Satz von gegenseitig interstitiell gedruckten Teilbildern gedruckt wird, wobei jedes Teilbild aus einem Satz von Punkten besteht, der Druckkopf Düsen, die eine Anzahl von Tröpfchen in Überlagerung aufspritzen, aufweist und jedes Tröpfchen aus einer mehrerer strahlungshärtbarer Zusammensetzungen zusammengesetzt ist, wobei die Tröpfchen auf dem Druckmedium verschmelzen und dabei den Punkt mit vorgegebener Graustufe bilden, und
• 4. ein Strahlungsmittel, mit dem die Punkte eines interstitiell gedruckten Teilbildes aktiv diffusionsfest gemacht werden.

The objects of the present invention are achieved by a method as defined in claim 1, wherein an image is printed on a print medium using radiation curable compositions by dot matrix printing, the method comprising the steps of:

• 1. Printing the image using the radiation-curable composition in the form of at least one set of mutually interstitially printed sub-images, each sub-image consisting of a set of dots, a dot composed of a number of superimposed droplets, and each droplet of one of a plurality of radiation-curable ones Compositions composed, wherein the droplets merge on the printing medium, thereby forming the point with a predetermined gray level, and
• 2. before printing a next sub-image from the set of sub-images, irradiating the points of the previous interstitially printed sub-image to make them actively migration-resistant.
• The objects of the present invention are also achieved by a device as defined in claim 10, which uses an image to be printed on a printing medium using radiation-curable compositions, the device comprising the following components:
• 3. a printhead which, using the radiation-curable composition, prints the image in the form of at least one set of mutually interstitially printed sub-images, each sub-image consisting of a set of dots, the printhead nozzles jetting a number of droplets in overlay , and each droplet is composed of one of a plurality of radiation-curable compositions, the droplets merging on the printing medium and thereby form the point with given gray level, and
• 4. a radiation means with which the points of an interstitially printed partial image are made actively diffusion-resistant.

The The present invention will now be described with reference to the following figures described.

SUMMARY THE FIGURES

1 shows a printing medium composed of a plurality of pixel locations, wherein a dot is formed of a plurality of droplets, which are each applied to one of the pixel locations according to an embodiment of the invention.

2 Figure 12 shows several dots attached to different pixel locations in multiple passes according to one embodiment of the invention, with dots attached in a later pass filling spaces between dots left unprinted during one or more previous passes.

3 12 shows several dots that have been applied to multiple pixel locations during multiple passes according to another embodiment of the present invention, wherein dots attached in a later pass overprint printed dots during one or more previous passes.

4a illustrates a 2 × 2 matrix superpixel with four overlapping equally sized dots, 4b is an enlarged view of the middle square of 4a ,

5 Figure 12 is a graph plotting contrast versus density of an example of dots consisting of droplets printed with four inks of different densities.

6 Fig. 12 is a very schematic illustration of an ink jet printer for use in the present invention.

7 is a schematic representation of a printer controller according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Even though the present invention will be described with reference to certain embodiments and figures, the present invention is not limited thereto only but on the claims. The present invention is primarily in the context of ink jet printing described, but not limited thereto. The like in the The term "pressure" used in the present invention is to be interpreted in a broad sense. He points to making markings on a print substrate by means of printing ink or other materials. Various suitable Printing methods for use in the present invention are described in the book "Principles of non-impact printing ", J.L. Johnson, Palatino Press, Irvine, 1998, e.g. Inkjet printing with deflected inkjet, ion projection pressure, field control pressure, Pulse inkjet printing, drop-on-demand inkjet printing (drop-on-demand inkjet printing) and high pressure ink jet printing. Particular preference is given to stop-free Printing method, without the present invention being limited thereto. The scope of the present invention includes any printing form, with the dots or droplets can be printed on a substrate, e.g. for printing polymer materials piezoelectric printheads used by Plastic Logic (http://plasticlogic.com/) for the Printing on thin-film transistors used and described. Accordingly, the term "printing medium" or "printing substrate" in a broad sense be interpreted and includes except paper, transparent sheet and textiles also flat plates or curved plates, the can be clamped in a printing press or fixed in the printing press and bottles, cups, plates, vases, glasses, bows, Ceramic figures, tiles and such materials of glass, plastic or ceramics to decorate. Furthermore, the pressure at Room temperature or elevated Temperature done.

In one embodiment of the invention, an image must be printed on a print medium, such as a transparency, using a radiation curable composition. In general, radiation-curable compositions contain a radiation-curable component, for example a monomer, oligomer or low molecular weight homopolymer, copolymer, terpolymer, graft copolymer or block copolymer, the sole requirement being that this component is replaced by radiation, eg electron beam ment, actinic radiation or ultraviolet radiation (UV radiation), hardened (polymerized). The composition may be printed in dissolved form or by reducing its viscosity at elevated temperature. In a preferred composition, the radiation-curable component is curable with ultraviolet radiation having a wavelength between 4 and 400 nm. In actinic radiation, the radiation-curable component is curable with actinic radiation having a wavelength between 4 and 600 nm. Radiation-curable compositions used in accordance with the invention may contain various ingredients, such as antioxidants, Pigments, dyes and crosslinking agents.

The printing medium is not required to absorb the radiation-curable composition to a high degree. Rather, it is preferred that the droplets remain liquid and agile enough on the surface of the pressure medium for sufficient time to allow superimposed drops to fuse. In addition, numerous radiation-curable compositions are used. The many different radiation-curable compositions can be compositions of the same dye or pigment, but with different density, and / or compositions of different dyes or pigments. UV-curable inks which are suitable for printing processes, and in particular ink-jet printing, are generally known in specialist literature, for example in US Pat US 4,303,924 . US 4,258,367 . US 5,889,084 in PCT Patent Application WO 99/02610 and in US Pat US 6,312,123 , Such inks are commercially available, eg a curable monomeric ink sold by Avecia, UK under the product name Pro-Jet Ultra Black Z2B. By diluting this ink with the ink solvent, which means, in addition to the colorant, all other compounds which together with the colorant make up the ink, inks of different shades of gray can be obtained.

Like it 1 shows, has a print medium 1 several pixel positions 2 on, ie p _1,1 to p _{n, m} . At a pixel position 2 a printhead sprays 10 a printing device 20 droplet 3 various radiation-curable compositions. All on one pixel position 2 sprayed droplets 3 make a point together 4 ,

• – 0 Tröpfchen der Zusammensetzung 1 + 15 Tröpfchen der Zusammensetzung 2
• – 1 Tröpfchen der Zusammensetzung 1 + 14 Tröpfchen der Zusammensetzung 2
• – 2 Tröpfchen der Zusammensetzung 1 + 13 Tröpfchen der Zusammensetzung 2
• – 3 Tröpfchen der Zusammensetzung 1 + 12 Tröpfchen der Zusammensetzung 2
• – 4 Tröpfchen der Zusammensetzung 1 + 11 Tröpfchen der Zusammensetzung 2
• – 5 Tröpfchen der Zusammensetzung 1 + 10 Tröpfchen der Zusammensetzung 2
• – 6 Tröpfchen der Zusammensetzung 1 + 9 Tröpfchen der Zusammensetzung 2
• – 7 Tröpfchen der Zusammensetzung 1 + 8 Tröpfchen der Zusammensetzung 2
• – 8 Tröpfchen der Zusammensetzung 1 + 7 Tröpfchen der Zusammensetzung 2
• – 9 Tröpfchen der Zusammensetzung 1 + 6 Tröpfchen der Zusammensetzung 2
• – 10 Tröpfchen der Zusammensetzung 1 + 5 Tröpfchen der Zusammensetzung 2
• – 11 Tröpfchen der Zusammensetzung 1 + 4 Tröpfchen der Zusammensetzung 2
• – 12 Tröpfchen der Zusammensetzung 1 + 3 Tröpfchen der Zusammensetzung 2
• – 13 Tröpfchen der Zusammensetzung 1 + 2 Tröpfchen der Zusammensetzung 2
• – 14 Tröpfchen der Zusammensetzung 1 + 1 Tröpfchen der Zusammensetzung 2
• – 15 Tröpfchen der Zusammensetzung 1 + 0 Tröpfchen der Zusammensetzung 2

In the present invention, each pixel position becomes 2 of the image on the print medium 1 occupied with a certain number of droplets, for example, each with the same number of droplets 3 the radiation-curable compositions used. By way of example 2 radiation-curable compositions can be used and can be any pixel position 2 with a one point 4 forming combination of 15 Droplets of these compositions are sprayed. This means that for every point 16 Color or density combinations are possible:

• - 0 droplets of the composition 1 + 15 droplets of the composition 2
• 1 droplet of composition 1 + 14 droplets of composition 2
• 2 droplets of composition 1 + 13 droplets of composition 2
• 3 droplets of composition 1 + 12 droplets of composition 2
• - 4 droplets of composition 1 + 11 droplets of composition 2
• - 5 droplets of composition 1 + 10 droplets of composition 2
• - 6 droplets of composition 1 + 9 droplets of composition 2
• 7 droplets of composition 1 + 8 droplets of composition 2
• - 8 droplets of composition 1 + 7 droplets of composition 2
• - 9 droplets of composition 1 + 6 droplets of composition 2
• - 10 droplets of composition 1 + 5 droplets of composition 2
• - 11 droplets of composition 1 + 4 droplets of composition 2
• - 12 droplets of composition 1 + 3 droplets of composition 2
• - 13 droplets of composition 1 + 2 droplets of composition 2
• - 14 droplets of composition 1 + 1 droplets of composition 2
• - 15 droplets of composition 1 + 0 droplets of composition 2

The to the formation of a point 4 deposited total number of droplets 3 is for every pixel position 2 exactly the same. All points 4 passing through the different droplets 3 at a pixel position 2 have been formed have the same diameter (eg 42.3 microns for a 600 dpi image). Be the different droplets 3 applied by wet-on-wet printing, they fuse immediately. Any of the various desired densities or colors may be obtained by blending the radiation-curable compositions in different proportions, for example, as per the list above.

According to embodiments of the invention, an image is printed in the form of a set of mutually interstitially printed sub-images. Among the terms "interstitial printing" or "interstitial mixed intermixing printing" used in the present patent application is meant hen an image to be printed is divided into a set of sub-images, each sub-image comprising printed parts and voids, and at least a portion of these voids present in one printed sub-image representing a print location for the printed parts of another sub-image and vice versa. In the present invention, two dots to be printed on adjacent pixel positions are not part of one and the same field. Accordingly, an image is printed in at least four passes in the present invention, wherein a sub-image is printed in each pass. In the discussion below, image is an image printed in four passes.

In a first pass, a first partial image is printed on the medium 1 written. Only the droplets are printed 3 , the points 4 at the pixel points 2 from, for example, straight columns and even rows. These pixel locations 2 are with pi, j in 1 where i and j are even numbers. After this print pass every point 4 actively rendered diffusion-resistant, for example by exposure to a UV lamp, when UV-curable ink is used as the radiation-curable composition. By "making one point diffusible" it is understood that it can no longer merge with any adjacent point, meaning that at least one dry skin forms on the point, while the inside of the point can remain fluid, so that when spraying In the case of an adjacent point both points can not bleed into each other and no mixing of colors occurs Instead of forming only a dry skin on the point, the point can also be solidified, ie the point as a whole is no longer liquid, but still contains solvents. Also, true point drying is possible, with all solvents removed from the solidified point It is clear that the various methods of diffusing a point above each require a different cure time, depending on the type of radiation curable composition used and the number of a single point forming droplet varies "To make a point actively diffusion-resistant" is understood to make the point faster diffusion-resistant than to naturally allow the point to become diffusion-resistant. By way of example, when using UV-curable inks, "to make a point actively diffusion-proof" means exposing the spot to a UV lamp, rather than allowing the spot to become diffusion-resistant by exposure to UV radiation in the environment.

After this step, in which points applied to the printing medium during the first pass are made diffusion-proof, a second sub-image is transferred to printing medium in a second pass 1 written. Here, for example, the points 4 on the pixel places 2 printed on the even rows in the odd columns and made non-diffusing. These pixel locations 2 are with pi, j in 1 where i is an even number and j is an odd number. Be the first points printed on the pixel locations pi, j with i and j as even numbers 4 not before the pressure of the points 4 made diffusion-resistant during the second pass, would merge with the points 4 adjacent pixel locations 2 occur, which would lead to bleeding and a false gray level.

In the same way, the points 4 on the pixel places 2 printed on the even rows and in the straight columns and made non-diffusing. These pixel locations 2 are with pi, j in 1 where i is an odd number and j is an even number.

Further, during the fourth pass, the points 4 on the pixel places 2 printed on the odd rows and in the odd columns and made non-diffusible. These pixel locations 2 are with pi, j in 1 where i and j are odd numbers.

In the above-described process, in the step of printing dot images, dots are set to pixel locations 2 dots are printed only at predetermined pixel locations, ie spots where dots are required to form a particular desired image. The blending step in printing a mutually interstitially printed sub-image is to apply smear marks only at other predetermined pixel locations, and only at those locations where such marks are required to form a desired image.

In the above example, the areas printed after four passes with points of the radiation-curable composition will see, depending on the type of composition used, as in 2 or 3 out. Each circle or part of a circle in 2 and 3 represents a point 4 on pixel spot 2 The numbers in the circles or circular parts refer to the number of passes during which the points 4 on the print medium 1 to be printed.

When using viscous radiation-curable compositions, each dot, once after the dots printed during the first pass, indicates 4 have been made non-diffusible, a be Aligned three-dimensional structure, for example, looks like a small cylinder, which from the print medium 1 protrudes. During the next pass, the radiation curable composition will flow into the gaps between these cylinders and will not receive true circular dots, but dots whose shape fills the space between the dots printed during the first pass, such as the dots printed in passage 2 2 demonstrate. Also during passes 3 and 4, points will fill up the voids left between neighboring points.

When using thinner radiation-curable compositions, the dots overlap and become the in 3 obtained result, wherein printed during a previous passage printed dots are partially covered by printed during subsequent passes points.

In of the present invention different inks are used, which is a dot overlap allow. From the whole range of possible Combinations of different densities can be a certain number chosen like 256 combinations, the grayscale is predetermined Characteristics such as stability. Under stability is the resistance to understand each gray level value against printing errors, e.g. the durability the density against errors in the accuracy of positioning each a pixel making point or in size control each Point or each point density.

The density D12 of an overlapping area between a first point with density D1 and a second point with density D2 can be calculated as follows: D 12 = D 1 + D 2 (Equation 1) or as a function of transparency, wherein the translucency T is represented as a function of the density D as T = 10 ^-D : T 12 = T 1 * T 2 (Equation 2)

The calculation of the density of in 4a shown superpixels, each point may have a different density, for example, according to the method described below. This method calculates the surface of each surface in 4b , which is an enlarged view of the middle square in 4a is. Formulas for calculating each surface will not be given below because they are known to those skilled in the art.

In the middle square of 4a each intersection between two points and each intersection of a point with the square is denoted by a two-digit number ij, eg 11, 12, ..., 16, 21, ..., 26, 31, ..., 36, 41, ..., 46, as shown in the enlarged view of 4b , wherein the first digit i indicates to which point the intersection belongs, and the second digit j represents a serial number. For each set of two consecutive points of intersection of a point i, one calculates the angle between the two points ij1 and ij2, relative to the center ci of the respective point i, eg for point 1, angle1_12 is calculated. This angle is the angle formed by the center c1 from point 1 between points 11 and 12 (generally referred to as angle i_j1j2).

For example, an origin O is chosen at the center c3 of point 3 as in 4b The coordinates of the points of intersection are calculated on the basis of the calculated angles Winkeli_j1j2, the distance ie in the horizontal direction between the centers of two neighboring points and the distance dv in the vertical direction between the centers of two neighboring points. Im in the 4a and 4b Although the example illustrated is equal to dh and dv, they usually can be different.

For each point i, the surfaces of the sections are calculated on the basis of the calculated angles Winkeli_j1j2, such as section i-j1j2, which in 4b is referred to as section 2_23.

On the basis of the calculated angles Winkeli_j1j2 and the rays of the points, the intersections between the points i1 and i2 are calculated, eg the intersection point3-point4 in 4b ,

It become the surfaces different triangles are calculated, such as triangle34_15_14, in combination with the respective calculated sections (which are added or subtracted become) the surface the respective areas result.

Since the surface of each pixel of the pixel printed with a certain density of ink is known (ie can be calculated), it is also possible to calculate the total density of the pixel, for example the pixel in 4a :

Ai is the area of the printed image with a single ink of density Di Pixels (ie the area with a transparency Ti), Aij is the one with two different ones Inks with density Di and Dj printed area of the pixel (ie the area with Transparency Ti and transparency Tj), Aijk the three different inks with density Di, Dj and Dk printed area of the Pixels (ie the area with the transparency values Ti, Tj or Tk), Aijkl is the one with four different inks with density Di, Dj, Dk and Dl printed area of the pixel (ie the area with the transparency values Ti, Tj, Tk and Tl respectively) and Aempty the non-inked area of the pixel. The total density is determined by the overlap of each pixel certainly. A certain density is obtained by adding all surfaces, multiplied by the transparency, and then determined the average over the total area.

The surface of the pixel corresponds to the following equation

through Equation 3 and Equation 4 leaves the density of a pixel for calculate every combination of points in the pixel.

The Results can ordered and the difference Δ between two consecutive values can be calculated. This Difference Δ becomes for example graphically plotted against the density in a curve and then compared to the Kanamori curve. So can the number of required Inks and their density. Based on the system the surfaces in combination with the different ink densities, the to obtain a particular curve most suitable inks are selected. Can do this Ink densities selected and over a rapprochement procedure be tried to get the best results.

Now the number of feasible gray levels for a pixel location 2 is calculated. For example, to print one of D droplets 3 (e.g., D = 16) Item 4 with a number I of radiation-curable compositions of different density or color (e.g., I = 4) may be the number of the different possible ones Densities or colors (ie grayscale GS) that coincide with a particular Number of radiation-curable compositions I and a certain number of droplets D by means of a mixing system described above can be realized as follows:

In this way, the minimum number of droplets needed to print 256 shades of gray can be calculated for a given number of radiation-curable compositions:
I = 2, then D = 255,
I = 3, then D = 22,
I = 4, then D = 10.

There in the above example, 16 droplets are combined at one point (D = 16), at least 4 radiation-curable compositions needed. In this case, 969 combinations are possible.

wobei D = Dichte des erhaltenen Punktes,
Dii = Dichte der strahlungshärtbaren Zusammensetzung Ii,
NIi = verwendete Anzahl der Tröpfchen der strahlungshärtbaren Zusammensetzung Ii.For each of these 969 combinations, the density is calculated as follows

where D = density of the point obtained,
Dii = density of the radiation-curable composition Ii,
NIi = number of droplets of the radiation-curable composition Ii used.

The Dense will be for each of the 969 possible Combinations calculated and arranged in ascending order. After that, the difference Δ between two neighboring densities corresponding contrast calculated in each point and, for example, plotted against the density in a curve. These Curve is then compared to the Kanamori curve.

The Kanamori curve shows a relationship between density differences and density, with the density difference at the given density being perceptible by the human eye. For each density, a minimum density difference is necessary to be noticeable. The Kanamori curve is the steady curve in 5 , From this figure it can be seen that for densities in the lower part of the curve, lower density differences are easier to perceive than for densities in the upper part of the curve. By way of example for a density 1, the density difference must be at least about 0.01 to be noticeable, while for a density 2 the density difference must be at least about 0.025. Therefore, lower densities require more grayscale than higher densities.

By change the densities of the different radiation-curable used Compositions can the in proportion to the Kanamori curve best composition densities are calculated.

5 Figure 12 shows a comparison of a plot of densities of combinations of four inks with the Kanamori curve. The density of the ink I1 = 3.75, the density of the ink I2 = 0.75, the density of the ink I3 = 0.15 and the density of the ink I4 = 0.03. It can be seen from the graph that it is possible to choose 256 values such that the difference between two consecutive values never exceeds the Kanamori curve. This means that a halftone can be realized so that no streaking is noticeable in the printed materials. If one were to obtain a graph with peaks exceeding the Kanamori curve, there is no combination for which this density (peak) can be achieved.

in the The above treatment is carried out after each passage, however, the present invention is not limited thereto. One Subpicture may require more than one pass. In such case will all passages a single sub-picture printed and then at least in part cured by radiation, before the printhead returns to the starting point and the next frame continues. This printing process is less preferred and that because drops over remain unirradiated on the printing material for a long period of time.

6 Figure 4 is a very schematic general perspective view of an ink jet printer useful in the present invention 20 , The printer 20 includes a carrier 31 , a carriage arrangement 32 , a stepper motor 33 , one through the stepper motor 33 powered transmission belt 34 and a guide rail assembly 36 for the carriage arrangement 32 , On cart arrangement 32 is a printhead 10 attached with several nozzles. To obtain the gray levels required by the present invention, printhead 10 and further comprising one or more ink cartridges containing radiation curable compositions or any delivery system for delivering radiation curable compositions. The radiation-curable composition-containing cartridges may contain a set of at least two different containers, each containing radiation-curable compositions having different gray-level values when printed For a particular printer, the printer becomes the printer 10 usually on a print medium 37 such as a transparency, guided along to print a so-called raster line extending in a first direction, eg across one side. The first direction is often referred to as a "fast scan direction." A raster line is from a series of through the nozzles of the printhead 10 on the print medium 37 built up sprayed points. The print medium 37 is usually intermittently by means of a (not shown) feed mechanism in a second, perpendicular to the first direction extending direction via a carrier 38 guided. The second direction is often referred to as a "slow scan direction".

The by step motor 33 powered transmission belts 34 moves the carriage assembly 32 in the fast scanning direction via the guide rail assembly 36 ,

The printer 20 is with a means 39 provided with a point is made actively diffusive. This agent 39 is selected depending on the type of the radiation-curable composition used to print the image. By way of example when using a UV-curable ink, the agent 39 a UV curing unit. The middle 39 can actively make the dots of a partial image diffusion-proof either after printing the entire partial image or during the printing of a part of the partial image. In the second case, a means 39 for example, to the carriage assembly 32 and then together with the printhead 10 continue to run and make the points just printed diffused. It is also possible that the means 39 regardless of the printhead 10 is operated (and consequently requires its own drive means) or is a fixed unit extending over the entire printing width. Anyway, it might be useful to have a radiation foil 40 between the printhead 10 and the agent 39 to arrange for solidification in the printhead 10 existing radiation-curable composition and thus blockage of the head 10 and to prevent conspicuousness of the printing process or so that already sprayed droplets, which form the next point to which, however, still further droplets are to be applied, are not rendered non-diffusible. This agent 39 For example, a radiation source such as a UV lamp and a focusing means which directs a beam such as a UV light beam to the surface of the printing medium printed with the inks may comprise. As a rule, the curing unit 39 as a neighbor element to the printhead 10 downstream.

7 is a block diagram of the electronic control system of a printer 20 , which is an example of a control system for use with a printhead according to the invention 10 is. The printer 20 contains a buffer memory 40 in which a print file in the form of from a host computer 30 supplied with signals, a frame buffer 42 in which print data is stored, and a printer controller 60 that control the overall operation of the printer 10 controls. To the printer controller 60 are a fast scan driver 62 for a carriage assembly drive motor 66 , a driver for slow sampling 64 for a paper feed drive motor 68 , a printhead driver 44 for the printhead 10 and a the operation of the curing station 39 Controlling driver for the curing unit 69 connected. There is also a data store 70 in which a look-up table or a similar system is stored in which the gray level to be printed is assigned the number of droplets to be printed for each type of radiation-curable composition used for a pixel location. host computer 30 may be any suitable programmable computing device, such as one with Intel Corp. US supplied Pentium II microprocessor-powered personal computer, for example, with a memory and a graphical interface such as that of Microsoft Corp. USA supplied Windows 98 Is provided. The printer controller 60 may include a computing device, such as a microprocessor, and may be, for example, a microcontroller. In particular, it may be a programmable printer controller, for example, programmable digital logic such as programmable array logic (PAL), a programmable logic matrix, and a programmable gate array, in particular a field programmable gate array (FPGA). The use of an FPGA allows subsequent programming of the printer device, eg by downloading the required settings of the FPGA.

The data store 70 Parameters to be saved can be from host computer 30 , eg via the on the host computer 30 running printer driver software, in data storage 70 be fed. By way of example, a printer driver of the host computer determines 30 the various parameters of the printing processes and thus acts on the printer control 60 then put the data in the data store 70 feeds. Based on these parameters, the printer controller reads 60 the information needed in the cache 40 stored print data is included, and sends control signals to the drivers 62 . 64 . 69 and 44 ,

By way of example, the print data are decomposed into individual color components in order to obtain image data in the form of a receive buffer memory for each color component 30 to get saved bitmap. Each bit of the bitmap is assigned a gray level. When supplied with by printer control 60 supplied control signals reads print head driver 44 the color component image data from frame buffer 52 off and then controls both the matrix (matrices) of the nozzles on the printhead 10 which then print the required number of droplets on the pixel locations as the curing unit 39 for curing the respective sprayed ink droplets.

As mentioned above, the printer control can 60 be programmable, eg equipped with a microprocessor or an FPGA. According to embodiments of the invention, a printer according to the invention may be programmed to obtain various complex gray level printing capabilities. By way of example, the basic model of the printer can offer a first number of gray levels and work with non-radiation curable normal inks. An upgrade in the form of an in the microprocessor or the FPGA of the printer control 60 downloading program can provide extra grayscale. Further, as an option, the use of a UV-curable ink can be programmed. Such option can then be selected either in the printer menu or via the host computer 30 be activated, in the latter case the program that drives the driver 69 the hardening unit controls, downloads or such already installed in advance, but still inactive program is activated. Accordingly, the present invention may be practiced with a computer program product that, when applied to a computing device, provides the functions of the various methods of the invention. Furthermore, a data carrier such as a CD-ROM or a floppy disk can be provided, on which the computer product can be stored in machine-readable form and which, when used on a computing device, performs at least one of the methods according to the invention. The computing device may include a microprocessor or an FPGA.

The data store 70 As known to those skilled in the art, it may include any suitable means for storing digital data, such as a register or set of registers, or a memory device such as RAM, EPROM, ROM, or other solid state memory.

Having illustrated and described the present invention by way of a preferred embodiment, it will be apparent to those skilled in the art that numerous changes or modifications are possible herein within the scope of the present invention as defined in the following claims. In reference to 7 For example, the parameters that determine the data required to print grayscale and / or use radiation-curable inks are stored in the data memory 70 saved. However, the print file used to perform the above-mentioned print embodiments may be processed by the host computer 30 be generated and the printer 20 then becomes an accessory to the host 30 just print this file accordingly. Consequently, the printing schemes according to the invention can be implemented in software on a host computer and printed on a printer executing the commands supplied from the host computer without error. Thus, a computer program product may be provided that provides the functions of the various inventive methods when installed on a computing device associated with a printhead, ie, the printhead and the programmable computing device may be provided with the printer or the programmable device may be a computer or computer system eg a LAN network connected to a printer (LAN = Local Area Network or Local Area Network). The printer can be a network printer. Furthermore, a data carrier such as a CD-ROM or a floppy disk can be provided on which the computer product can be stored in machine-readable form and which, when the program stored on the data carrier is carried out, can execute at least one of the inventive methods on a computer. The computing device may be a personal computer or an FPGA.

Claims (10)

A method in which an image is printed on a print medium using radiation curable compositions by dot matrix printing, the process comprising the steps of: printing the image using the radiation curable composition in the form of at least one set of mutually interstitially printed subimages, each A set of sub-images, wherein - two dots to be printed on adjacent pixel locations are not part of the same sub-image, and wherein - each sub-image consists of printed dots and spaces, and wherein - at least a portion of the voids in a printed sub-image occupy a location for the printed dots another sub-image, wherein one point is composed of a number of superimposed droplets and each droplet is composed of one of a plurality of radiation-curable compositions, wherein the droplets fuse on the print medium thereby forming the dot of predetermined gray level, and before printing a next frame of the set of frames, irradiating the dots of the previous interstitially printed frame to make them actively migration-resistant. Method according to claim 1, characterized in that that a partial image formed in a passage of a printhead becomes. Method according to claim 1 or 2, characterized that the step in which the points are made actively diffusion-resistant be the formation of at least one dry skin on the points includes. Method according to one of the preceding claims, characterized characterized in that the step in which the points are actively diffusion-resistant which includes solidification of the points. Method according to one of the preceding claims, characterized characterized in that the step in which the points are actively diffusion-resistant which includes drying the dots. Method according to one of the preceding claims, characterized characterized in that the radiation-curable composition is a UV-curable Ink is. Method according to Claim 6, characterized that one point is UV-curable Ink by irradiating the dot with a UV lamp Light is made diffusion-resistant. Method according to one of the preceding claims, characterized characterized in that at least two radiation-curable compositions with different shades of gray are used. Method according to one of the preceding claims, which further comprising a step in which the number of droplets of each of the different radiation-curable sprayed on each other Compositions based on the Kanamori curve is determined. Apparatus for printing an image on a print medium using radiation-curable compositions, the device containing the following components - A pressure medium, with the using the radiation-curable Composition the picture in the form of at least one sentence of each other printed interstitial printed sub-images, where - two up dots to be printed at adjacent pixel locations do not have a part and are the same field and where - each partial image printed Points and voids and wherein - at least a part of the voids in a printed drawing file, a place for the printed dots of another Partial image forms, the pressure medium with nozzles, the a number of droplets in overlay apply, stocked is and every droplet from one of several radiation-curable Composition is composed, wherein the droplets on merge the print medium while a point with predetermined Form greyscale, and - one Radiation with which the points of an interstitially printed Partial image actively made to be diffusion-resistant, before the next field is printed.